A prior art DBF radar apparatus comprises: a transmitter section for radiating an electromagnetic wave as a transmit signal; an array antenna comprising a plurality of antenna elements for receiving, as a received signal, the electromagnetic wave reflected by an object; a plurality of input terminals connected to the respective antenna elements; an output terminal which is selectively connected by a switching means to one of the plurality of input terminals; and a receiver section in which the received signal obtained from the output terminal is downconverted by using a portion of the transmitted signal and the difference signal, representing the difference between the transmitted signal and the received signal, is converted into a digital signal, wherein the distance to or the relative velocity of the object is detected by applying prescribed processing to the digital signal obtained from the receiver section (JP H11-160423 A).
There is also disclosed a radar apparatus in which each antenna is sequentially connected, thereby eliminating the need to provide an RF receiver circuit for each antenna (JP H11-64485 A).
Further, in a radar apparatus in which each antenna is sequentially connected, it is disclosed that one antenna is set as a reference antenna and a beat signal produced from the signal received by the reference antenna is used for phase correction when combining signals by DBF (JP H11-311668).
There is disclosed a radar apparatus in which the receiver section includes a receive switch for sequentially selecting a plurality of receiving antennas, one at a time, by a select signal so that the receiver that generates a beat signal by mixing the received signal with a local signal is shared among the plurality of receiving antennas in a time-division fashion (JP2000-284047).
There is also disclosed a radar apparatus which transmits a frequency-modulated signal after switching it by a first switching signal, receives the signal reflected by a target object, mixes the received signal with the transmitted signal after switching the received signal by a second switching signal, and measures the distance and the relative velocity of the target object, based on the beat signal obtained, by further mixing the signal with a third switching signal (JP2003-172776).